The experimental study on thermocapillary convection in liquid bridges of large Prandtl number has been carried out on Tiangong-2 in space. The purpose of these experiments is to study the oscillation instability of thermocapillary convection, and to discover and recognize the mechanism of destabilization of thermocapillary convection in the microgravity environment in space. In this paper, the geometry of a half-floating-zone liquid bridge is featured by the aspect ratioArand volume ratioVr, and its influence on critical conditions of oscillatory thermocapillary convection is studied. More than 700 sets of space experiments have been finished. The critical conditions and oscillation characteristics of thermocapillary convection instability in theAr–Vrparameter space have been fully obtained under microgravity conditions for the first time. It is found that theAr–Vrparameter space can be divided into two regions of different critical conditions and oscillation characteristics: the region of low frequency oscillation, and the region of high frequency oscillation. More importantly, we obtain the complete configuration of these two stability neutral curves, and find that the low frequency mode is a ‘’ type curve. Based on this, we discuss the influence of heating rate on the oscillation mode. It is found that the heating rate affects the selection of critical mode, which results in a jump change of critical temperature difference. The findings of this study are helpful to better understand the critical modes and transition processes of thermocapillary convection in liquid bridges with different configurations.

We carried out space experiments on thermocapillary convection in liquid bridges with large Prandtl number in the Tiangong-2 space laboratory, studying the influence of geometrical parameters, including aspect ratio (Ar, height to diameter) and volume ratio (Vr). It is found that there are two modes of temperature oscillation in thermocapillary convection in liquid bridges: low- and high-frequency oscillation, corresponding to different critical temperature difference and geometrical parameters, respectively. In this paper, the geometrical effect on the wave pattern and its transformation in the oscillating thermocapillary flow is studied in detail. Temperature signals from thermocouples on five measuring spots are analyzed to distinguish different oscillation modes corresponding to characteristics of azimuthal waves, such as wave number, traveling wave, and standing wave. Under a small volume ratio, the low-frequency traveling wave mode transits to the high-frequency standing wave mode; under a large volume ratio, the high-frequency standing wave has abundant mode transformations, such as standing wave → traveling wave, standing wave → traveling wave → standing wave, and so on, and the transformation process of the wave mode is sensitive to the aspect ratio.

A fluid experiment was conducted on China’s SJ10 satellite to assess the instability of thermocapillary convection under microgravity. Oscillations of thermocapillary convection in an annular pool were investigated when the difference in temperature exceeded a certain threshold. Dynamics and transitions of the wave pattern were observed using an infrared camera. This work is concerned with the effect of the surface configuration on the wave patterns. There are 3 types of surface configurations that depend on the volume ratio: Vr < 0.77 (zone 1), 0.77 < Vr < 1 (zone 2), and Vr > 1 (zone 3). An irregular local wave occurs at Vr < 0.65, and a regular azimuthal wave occurs at Vr > 0.65. We observed the regular wave with the wavenumber m = 3 in zone 1 and zone 3 and the competition between m = 3 and m = 4 in zone 2. The nonlinear dynamics of traveling waves, standing waves, and counterpropagating waves were studied. The standing wave appears near the onset and transitions to the traveling wave. With a similar mechanism, counterpropagating waves with m = 3 and m = 4 occur in some cases at the onset. Additionally, counterpropagating waves also act as a transitional mode when the traveling wave transitions from m = 4 to m = 3. The traveling wave is very stable, but it develops into standing waves or Benjamin-Feir instability under highly supercritical conditions.

Thermocapillary convection has always been a hot topic of great importance in either crystal growth or thin films science. A space experiment about thermocapillary convection in an open cylindrical annuli pool will be done on SJ-10 satellite. A payload for space experiment has been established, which includes a cylindrical annuli thermocapillary convection system, a thermocouple temperature controlling system and measurement system, a thermal infrared imager, a high-precision displacement sensor, and an experiment controlling system. Some experiments have been done on the ground in order to compare with the results of space experiment. Some results from the ground experiment are shown, such as temperature oscillation, surface oscillation, and flow pattern transfer.

This paper addresses the problem of designing an active disturbance rejection controller for a high accuracy drag-free satellite with cubic test mass. The uncertain model of the drag-free satellite is defined. The performance requirement imposed on the acceleration of the test mass is broken down into specification of drag-free and suspension loop because of the disturbance decoupling controller, which is based on the linear active disturbance rejection control technique. We derive two-degree internal model control structure of ADRC, which is used for robust stability verification. Search programs determine the parameters that satisfy system stability and the performance requirement. The design technique has shown to be robust to the perturbation of the system and good performance in disturbance suppressing. To check the design of the controller, an overall simulation is preformed, and the results confirmed that the controller is able to meet the system requirements.